Get a bob sled, single feed, allow alittle time between shots. Dont let the round warm up in the chamber. Do some slow firing and see if that makes any difference.
You dont need a crimp, just enough neck tension to hold the bullet in place.
Brass prep does make a noticeable difference in ARs too, done it, still do it.
How much play is there between your upper and lower? If there is any movement that will cause this issue. The fix is shims. I posted a a big something about AR accuracy while back, if you can find it its worth a read. Its jmo, but its worked for me and Ive yet to see an AR outshoot mine. Several tips and tricks to play with. Theres so many could be issues you just gotta start from building it and pull every trick in the book to feel satisfied you remedied things.
Square receiver face, torques on everything, run it wet, gas flow, how clean is it, trigger, shims, your rest, your grip plays a factor shooting, list goes on.